Conventionally, many types of cards such as identification cards, driving licences and membership cards carry thereon various items of information to provide a disclosure of what the bearers are. Of the most importance for ID cards in particular are literal information such as name and address and a photographic image of face.
One classical technique for applying a photograph of face to each of various cards involves bonding it to a given region of the card with an adhesive. Problems with this technique are that it is very laborious; it makes the surface of the card uneven and so rids it of flatness; and it allows the card to be easily counterfeited or falsified by the replacement of .another photograph of face.
In order to solve the defect of such an old technique as mentioned above, there has been developed a sublimation transfer type of imaging technique.
According to this heat transfer technique, a sublimation type of heat transfer sheet formed by providing onto the surface of a substrate film a layer containing a dye sublimable and transferable by heat is overlaid on a card substrate., and the assembly is heated from the back side of the sublimation transfer sheet with a thermal head to reproduce a photograph of face on the card substrate simultaneously with printing of various letters, characters and so on. Alternatively, these characters may be printed in a hot meltable ink type of heat transfer manner. In either case, this technique has the advantage of being able to be carried out with a simple thermal printer. Since various items of information obtained by the above heat transfer technique are less than satisfactory in terms of such properties as rub resistance, however, the surface of the photograph, etc. is generally provided with a transparent surface protecting layer excelling in such properties as rub resistance.
Especially because the photograph is formed by fixing the dye in the card substrate, the card obtained by the above technique is of improved flatness and provides greater security against falsifying and counterfeiting. Even with this technique, however, there is a little fear that the photograph and other information may be falsified or counterfeited by removing the protecting layer by solvents, acids, bases or the like.